It might be late but that is because April's application of the month covers one of the finest additions to KDE 3.4: KPDF. The application overview takes us through the powerful features in KPDF: thumbnails, contents, scrolling, zooming and searching. We also have an interview with one of the creators of KPDF, Albert Astals Cid. He tells us how KPDF got started, about Free Software use in Spain and where we should visit on our way to Málaga. Enjoy App of the Month in Dutch, English, French or German.

Not that I know of, however they are working on providing better text selection (sometimes text selection in PDFs doesn't work like you would expect). Also, I believe KWord has a PDF import filter; not sure how well it works.

I think that would be outside the scope of KPDF. Maybe improving the KWord import filter would be a better idea.
Anyway, I really do hope they add to KPDF Postscript support, so it can be THE universal viewer for KDE, and drop KGhostview which right now is a bit redundant.

I'm currently working on a (highly proprietary corporate internal) application that mangles PDFs in various ways. It's not technically difficult to modify the PDF document structure (a complete document structure parser which can read a PDF file, mangle its internal structure, and write a new PDF file is two weeks' effort and about 1300 lines of Perl). It is a little difficult to do this in open-source land while also respecting the egregious licensing terms of the PDF spec documents (most of which IMHO are probably unenforceable, but Adobe tries to enforce them anyway).

Most of the PDF document structure is above the page level. To PDF, the pages you can actually see are just leaf nodes in a big multiple overlapping tree structure. Most of the structure deals with page indexes, bookmarks, hyperlinks, annotations, fonts, images, and structural details to support incremental revision by appending to the file and efficient document loading over slow/high-latency links (but not both at the same time). Adobe has a number of patents on those topics.

I expect the first useful editing features to be rearranging pages, changing the bookmarks list, importing pages from other documents, adding annotations and hyperlinks, and limited graphics or text manipulation such as adding a page number, headers/footers, border, logo or watermark to pages--all easy features to implement on top of a working PDF parser/generator.

I believe the text-part of koffice can import pdf's. I don't know how good the support is ...

Kpdf is a nice application. I used it lately a bit. I hope that they can make the rendering go faster and that they test it on papers that contain mathematical expressions. For papers that contain mathematical expressions, I (sometimes) switch to xpdf since it renders the formulas well. Just searching for papers on scholar.google.com or some other source that contain formulas may be a start ...

for the rest, nice work!!! I like the menu where you can choose between selecting character-data or image-data, ...

I always end up using acroread, since it lets me rotate the documents so that I can read them full screen on my tablet convertable acer travelmate. I would have guessed rotation to be a standard feature for such a program, but kpdf seems to lack it.

Seconded. Today I had to read a document that is rotated 90 degrees. I just realized that neither kpdf nor evince provides rotation, so I had to install acroread. But to give credits where it's due, for regular PDFs I do use kpdf on a daily basis.

Of course, we're in 2008 now and shouldn't be talking about kdpf anymore, but okular, which actually _does_ provide rotation. And then... If using a convertible tablet is the reason one wants to rotate the display of a pdf, why not use xrandr to rotate the whole display?

While I like the overall feeling of kpdf I usually switch back to acroread for longer texts. Why? The fonts are a lot nicer and better to read. A closer look with xmag shows that compared to acroread the fonts are bold. Btw xpdf produces exactly the same results as kpdf.
Any chance that the fonts will be rendered more like acroread in future versions or is there a reason why its different?

I have no real need for editing of PDFs, but the ability to add annotations - underlines, marginal notes, highlighting - would be extremely useful. They could be added to the PDF itself, or stored as a separate "overlay" in whatever format.

I have looked for this feature in various applications, and the only programs that support it are scribus-like applications, which try to load the whole document at once, rendering them useless for documents that consist of (say) four hundred pages scanned at 600 DPI. (Of course, DjVu is a good format for this, but none of the programs supporting it permit annotations either.)